adywan said:

Plus there is a deleted scene from ESB where Luke and Leia move in for a kiss in the medical bay. If she was indeed intended to be his sister all along then George is one twisted guy ;

I agree. As far as the Luke/Leia angle goes, the way the footage shown on this particular ESB trailer at 0:49 secs (where we hear the words 'It's an epic of romance') is filmed, definately gave me the impression that Luke and Leia were not originally intended to be brother and sister at this point... And still does.

http://www.youtube.com/watch?v=9utBrJhfw60

The scene that ended up in the movie is innocent enough as it's obvious Leia is merely trying to make Han jealous...but I still don't buy that this was because GL had it in mind at this point for them to discover they were siblings eventually. The way things look in the trailer puts paid to that notion, as far as I'm concerned.